Certain types of lighting fixtures are designed to be mounted directly adjacent a ceiling or wall and are typically made with a rather small housing. The word "small", of course, is a relative term; but in this context it refers to a luminaire which is capable of containing a relatively large lamp, such as a high intensity discharge lamp or a fluorescent tube, and in which the housing is not large as compared with the lamp.
Another characteristic of a fixture of this type which is significant is that the fixture is made to "hug" the wall or ceiling against which it is mounted, presenting a relatively unobtrusive, and yet attractive, appearance.
If such a fixture is to be made using a high intensity discharge (HID) lamp, which requires the use of a ballast or transformer and other circuit components, a considerable amount of heat is generated within the housing by the lamp itself and also by the ballast. Conventionally, a fixture of this type is constructed using a metal housing, often with a glass refractor, the metal housing being capable of dissipating the heat generated by the lamp and ballast so that the temperature does not become excessive. It is, however, desirable to be able to make the housing entirely of polymeric material because such material is less expensive to fabricate in large quantities and because the use of molded polymeric materials permits wider variety in the choice of designs and configurations which can be used to accommodate a wide variety of decorating schemes, and to be able to make the housing substantially closed to keep out dirt.